At the present time, the surface density of commercially available optical disk devices is on the order of about 880 megabits per square inch. A surface density capable of being generally realized at the research and development level while overcoming the strict environmental conditions for using optical disk devices is said to be about three times as high as the surface density realized at the product level. In commercially available optical disk devices, a wavelength of 780 nm is used, the numerical aperture (NA) of the objective lens is 0.55, mark length recording is used as a recording system, and continuous servo is used as a servo system. "Standard ECMA-195" is a reference article by ECMA (European Computer Manufacturer Association) containing standards for data interchange on 130 mm optical disk cartridges.
An object of the present invention is to realize the highest density recording/reproducing characteristic of an optical disk while using constituent elements which are realizable at the present time. A recording density of 10 Gbit/in.sup.2 can be realized.